1. Field of the Invention
This invention relates to a silencer arranged in a gas flow passage of an exhaust gas system, blower or the like, to reduce sound or noise transmitting through gases in the passage.
2. Description of the Prior Art
In order to reduce the sound transmitting through a gas in a gas flow passage, silencers located in the passages have been widely used, wherein sound absorbing materials are attached to desired inner surfaces of a suitable number of the gas flow passages provided in duct casings. With such silencers, however, the sound absorbing materials are likely to be damaged by high speed gas flows, and dust in the gas flows is apt to adhere and accumulate onto surfaces of the sound absorbing materials so as to reduce their sound absorbing coefficients and diminish their acoustic absorptivity for a short period of time. Moreover, there have been attempts to arrange a series of plates having apertures on inner surfaces of sound absorbing material to prevent the material from being damaged. In this case, however, as the dust in gas flow is more prone to accumulate at the apertures of the sound absorbing plates, the rapid diminishing of the acoustic absorptivity due to the accumulation of dust is not eliminated. Accordingly, it has been expected in this industrial field to obtain a silencer capable of maintaining its sound absorbing coefficient at its initial high level without damage to a sound absorbing material.